This project is designed to investigate the size and spatial distribution of cortical "colonies" that are associated with individual muscles or closely related groups of muscles, as well as the activity of neurons in such colonies in the motor cortex and supplementary motor area during defined voluntary motor behaviors. Intracortical microstimulation (ICMS) is used to map regions that produce excitation or inhibition of particular muscles or muscle groups, and the resultant cortical maps are compared with these for synergist muscle groups. Cortical cell discharge patterns during normal movements is evaluated with respect to the excitation or inhibition of muscle activity that is produced by ICMS. A pilot study of the histochemistry of monkey forearm muscles has been initiated.